Bai Qiao Original: omnipotent type boost: any

4.6 use third-party LibrariesThe preceding section describes how to assign values to, convert, and convert character codes to Visual C ++. In fact, there are some useful third-party class libraries to help C ++ programmers complete object processing, boost is a famous one. This section briefly introduces boost: any, boost: lexical_cast, and rational boost: rational in the boost library.4.6.1 universal boost: anyThe boost Library provides the any class. boost: any is a class that can save any type value. This is a bit like the variant type. However, because variant uses a huge union, low efficiency. While boost uses the template, it does not change the type of the value during saving, but only provides a method for the user to determine the type and value when necessary. Boost: any can be used to store almost any data type:

 
 

  
  
boost::any ai, as;  
  
  
ai = 100;  
  
  
as = string("hello"); 
 
 

When necessary, we can use any_cast to restore the original data:

 
 

  
  
int i = boost::any_cast<int>(ai);  
  
  
string s = boost::any_cast<string>(as); 
 
 

When this type of conversion does not match, bad_any_cast will occur abnormally:

 
 

  
  
try 
  
  
{  
  
  
    int i = boost::any_cast<int>(as);  
  
  
}  
  
  
catch(boost::bad_any_cast & e)  
  
  
{  
  
  
} 
 
 

In traditional C ++ programs, we have to use the omnipotent Pointer "void *" to support various data types, but unfortunately, the Conversion Based on universal pointers is insecure. The "void *" type check is missing. Therefore, we recommend that you use the any class whenever possible. Now you can write the following program to experience how to use boost: any to convert object types. Program 4-10: Use boost: any to convert Object Types

 
 

  
  
01  #include "stdafx.h" 
  
  
02  #include "boost/any.hpp" 
  
  
03  #include <string>  
  
  
04    
  
  
05  using namespace std;  
  
  
06  using namespace boost;  
  
  
07    
  
  
08  class Cat  
  
  
09  {  
  
  
10  };  
  
  
11    
  
  
12  void print(any it)  
  
  
13  {  
  
  
14      if(it.empty())  
  
  
15      {  
  
  
16          printf("nothing!\r\n");  
  
  
17          return;  
  
  
18      }  
  
  
19    
  
  
20      if(it.type() == typeid(int))  
  
  
21      {  
  
  
22          printf("integer: %d\r\n", any_cast<int>(it));  
  
  
23          return;  
  
  
24      }  
  
  
25    
  
  
26      if(it.type() == typeid(string))  
  
  
27      {  
  
  
28          printf("string: %s\r\n", any_cast<string>(it).c_str());  
  
  
29          return;  
  
  
30      }  
  
  
31    
  
  
32      if(it.type() == typeid(CString))  
  
  
33      {  
  
  
34          _tprintf(_T("CString: %s\r\n"), any_cast<CString>(it));  
  
  
35          return;  
  
  
36      }  
  
  
37    
  
  
38      if(it.type() == typeid(Cat))  
  
  
39      {  
  
  
40          _tprintf(_T("oops! a cat!\r\n"));  
  
  
41          return;  
  
  
42      }  
  
  
43  }  
  
  
44    
  
  
45  int main()  
  
  
46  {  
  
  
47      print(100);  
  
  
48    
  
  
49      any as[] = {any(), 100, string("hello"), CString("world"), Cat()};  
  
  
50      for(int i = 0; i < sizeof(as) / sizeof(as[0]); i++)  
  
  
51      {  
  
  
52          print(as[i]);  
  
  
53      }  
  
  
54    
  
  
55      return 0;56 } 
 
 

The result output is 4-18.
650) this. width = 650; "onclick = 'window. open (" http://blog.51cto.com/viewpic.php? Refimg = "+ this. src) 'alt =" "src =".../attachment/200908/200908241251094430129 .jpg" border = "0"/>
========================================================== === 650) this. width = 650; "onclick = 'window. open ("http://blog.51cto.com/viewpic.php? Refimg = "+ this. src) 'alt =" "src =" http://book.vcer.net/images/vcmap-s.gif "/> the above is from section 4.6.1

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